Persistent Intermitted Payment Receipt Failures

-- url of the page with the problem -- : shop.justducks.co.uk
-- HikaShop version -- : 3.1.1
-- Joomla version -- : 3.7.3
-- PHP version -- : Latest
-- Browser(s) name and version -- : All

We are experiencing persistent but sporadic order payment issues.

Using PayPal Hosted, starting early last week (mid-July), orders were "created" in HS and the payment processed as "paid" by PayPal.

However, the order status stays in the "created" state and does not upgrade to the "paid" status.

The attached documents has the email message and the last section of the debug log

Please advise as to a possible solution to this issue.